Protective headgear and helmets have been used in a wide variety of applications and across a number of industries including sports, athletics, construction, mining, military defense, and others, to prevent damage to a user's head and brain. Damage and injury to a user can be prevented or reduced by helmets that prevent hard objects or sharp objects from directly contacting the user's head. Damage and injury to a user can also be prevented or reduced by helmets that absorb, distribute, or otherwise manage energy of an impact.
Protective headgear and helmets sometimes comprise multiple layers of energy management materials. In some instances, helmets comprising multiple layers of energy management materials have included lubricants or extra low-friction layers or liners disposed between the multiple layers of energy management materials. The lubricants or extra low-friction layers or liners have been used to provide relative movement, slipping, or rotation between the two energy management liners.